Disposable absorbent products (e.g., diapers, feminine hygiene products, incontinence products, etc.) are subjected to one or more liquid insults, such as of water, urine, menses, or blood, during use. Many commercially available diapers allow water vapor to pass through the diaper and into the environment to lessen the amount of moisture held against the skin and reduce the chance of skin irritation and rash due to skin overhydration. To allow the passage of vapor through the diaper and into the environment while holding liquid, a “breathable” outer cover is often employed that is formed from a nonwoven web laminated to a film. The film contains a filler (e.g., calcium carbonate) that causes a series of micropores to develop in the film when stretched. The micropores form what is often referred to as “tortuous pathways” through the film. Liquid contacting one side of the film does not have a direct passage through the film. Instead, a network of microporous channels in the film prevents liquids from passing, but allows gases and water vapor to pass.
One shortcoming with such microporous films is that they are generally formed from polyolefins (e.g., LLDPE), which are not biodegradable. Consequently, various attempts have been made to form microporous films from biodegradable polymers. Problems have been encountered, however, in forming microporous biodegradable films with a high breathability. Specifically, biodegradable polymers normally have a density that is greater (e.g., 30% greater) than the density of conventional polyolefins. Thus, when blended with such biodegradable polymers, the filler actually occupies a higher volume than it would otherwise occupy when blended with polyolefins at the same weight percentage. Due to this higher relative volume, the “ceiling” or maximum amount of filler that can be added to the film, without undesirably increasing the film modulus and reducing film stretchability, is lowered. However, because high breathability is normally achieved by using a high level of filler, the lower “ceiling” of the filler limits the extent to which the breathability of the biodegradable film may be increased using conventional techniques. Another complicating factor is that many biodegradable polymers are also tackier than polyolefins. This tackiness makes it difficult for the polymer to release or debond from the filler particles, thereby resulting in smaller pores, which leads to lower breathability. Further, attempts to enhance breathability by increased stretching typically results in an increased number of film defects (e.g., holes) that result in breaks and/or reduced tensile properties.
As such, a need currently exists for a technique of improving the breathability of biodegradable films.